Ceasing his restless walk up and down the room, Tom Swift strode to the window and gazed across the field toward the many buildings, where machines were turning out the products evolved from the brains of his father and himself. There was a worried look on the face of the young inventor, and he seemed preoccupied, as though thinking of something far removed from whatever it was his eyes gazed upon.

"Well, I'll do it!" suddenly exclaimed Tom. "I don't want to, but I will. It's in the line of 'doing my bit,' I suppose; but I'd rather it was something else. I wonder--"

"Ha! Up to your old tricks, I see, Tom!" exclaimed a voice, in which energy and friendliness mingled pleasingly. "Up to your old tricks!"

"Oh, hello, Mr. Damon!" cried Tom, turning to shake hands with an elderly gentleman--that is, elderly in appearance but not in action, for he crossed the room with the springing step of a lad, and there was the enthusiasm of youth on his face. "What do you mean--my old tricks?"

"Talking to yourself, Tom. And when you do that it means there is something in the wind. I hope, as a sort of side remark, it isn't rain that's in the wind, for the soldiers over at camp have had enough water to set up a rival establishment with Mr. Noah. But there's something going on, isn't there? Bless my memorandum book, but don't tell me there isn't, or I shall begin to believe I have lost all my deductive powers of reasoning! I Come in here, after knocking two or three times, to which you pay not the least attention, and find you mysteriously murmuring to yourself.

"The last time that happened, Tom, was just before you started to dig the big tunnel-- No, I'm wrong. It was just before you started for the Land of Wonders, as we decided it ought to be called. You were talking to yourself then, when I walked in on you, and-- Say, Tom!" suddenly exclaimed Mr. Damon eagerly, "don't tell me you're going off on another wild journey like that--don't!"

"Why?" asked Tom, smiling at the energy of his caller.

"Because if you are, I'll want to go with you, of course, and if I go it means I'll have to start in as soon as I can to bring my wife around to my way of thinking. The last time I went it took me two weeks to get her to consent, and then she didn't like it. So if--"

"No, Mr. Damon," interrupted Tom, "I don't count on going on any sort of a trip--that is, any long one. I was just getting ready to take a little spin in the Hawk, and if you'd like to come along--"

"You mean that saucy little airship of yours, Tom, that's always trying to sit down on her tail, or tickle herself with one wing?"

"That's the Hawk!" laughed Tom; "though that tickling business you speak of is when I spiral. Don't you like it?"

"Can't say I do," observed Mr. Damon dryly.

"Well, I'll promise not to try any stunts if you come along," Tom went on.

"Where are you going?" asked his friend.

"Oh, no place in particular. As you surmised, I've been doing a bit of thinking, and--"

"Serious thinking, too, Tom!" interrupted Mr. Damon. "Excuse me, but I couldn't help overhearing what you said. It was something about going to do something though you didn't want to, and that it was part of your 'bit'. That sounds like soldier talk. Are you going to enlist, Tom?"

"No."

"Um! Well, then--"

"It's something I can't talk about, Mr. Damon, even to you, as yet," Tom said, and there was a new quality in his voice, at which his friend looked up in some surprise.

"Oh, of course, Tom, if it's a secret--"

"Well, it hasn't even got that far, as yet. It's all up in the air, so to speak. I'll tell you in due season. But, speaking of the air, let's go for a spin. It may drive some of the cobwebs out of my brain. Did I hear you say you thought it would rain?"

"No, it's as clear as a bell. I said I hoped it wouldn't rain for the sake of the soldiers in camp. They've had their share of wet weather, and, goodness knows, they'll get more when they get to Flanders. It seems to do nothing but rain in France."

"It is damp," agreed Tom. "And, come to think of it, they are going to have some airship contests over at camp today-- for the men who are being trained to be aviators, you know. It just occurred to me that we might fly over there and watch them."

"Fine!" cried Mr. Damon. "That's the very thing I should like. I'll take a chance in your Hawk, Tom, if you'll promise not to try any spiral stunts."

"I promise, Mr. Damon. Come on! I'll have Koku run the machine out and get her ready for a flight to Camp. It's a good day for a jaunt in the air."

"Get out the Hawk, Koku," ordered the young inventor, as he motioned to a big man--a veritable giant--who nodded to show he understood. Koku was really a giant, one of a race of strange beings, and Tom Swift had brought the big man with him when he escaped from captivity, as those will remember who have read that book.

"Going far, Tom?" asked an aged man, coming to the door of one of the many buildings of which the shed where the airship was kept formed one.

"Not very far, Father," answered the young inventor. "Mr. Damon and I are going for a little spin over to Camp Grant, to see some aircraft contests among the army birdmen."

"Oh, all right, Tom. I just wanted to tell you that I think I've gotten over that difficulty you found with the big carburetor you were working on. You didn't say what you wanted it for, except that it was for a heavy duty gasolene engine, and you couldn't get the needle valve to work as you'd like. I think I've found a way."

"Good, Dad! I'll look at it when I come back. That Carburetor did bother me, and if I can get that to work-- well, maybe we'll have something soon that will--"

But Tom did not finish his sentence, for Koku was getting the aircraft in operation and Mr. Damon was already taking his place behind the pilot's seat, which would be occupied by Tom.

"All ready, are you, Koku?" asked the young inventor.

"All ready, Master," answered the giant.

There was a roar like that of a machine gun as the Hawk's engine spun the propeller, and then, after a little run across the sod, it mounted into the air, carrying Tom and Mr. Damon with it.

"Mind you, Tom, no stunts!" called the visitor to the young inventor through the speaking tube apparatus, which enabled a conversation to be carried on, even above the roar of the powerful engine. "Bless my overshoes! if you try, looping the loop with me--"

"I won't do anything like that!" promised Tom.

Away they soared, swift as a veritable hawk, and soon, after there had unrolled below their eyes a succession of fields and forest, there came into view rows and rows of small brown objects, among which beings, like ants, seemed crawling about

"There's the Camp!" exclaimed Tom.

"I see," and Mr. Damon nodded.

As they approached, they saw, starting up from a green space amid the brown tents, what appeared to be big bugs of a dirty white color splotched with green.

"The aircraft--and they have camouflage paint on," said Tom. "We can watch 'em from up here!"

Mr. Damon nodded, though Tom could not see him, sitting in front of his friend as he was.

Up and up circled the army aircraft, and they seemed to bow and nod a greeting to the Hawk, which was soon in the midst of them. Tom and Mr. Damon, flying high, though at no great speed, looked at the maneuvers of the veterans and the learners--many of whom might soon be engaging the Boches in far-off France.

"Some of 'em are pretty good!" called Tom, through the tube. "That one fellow did the loop as prettily as I've ever seen it done," and Tom Swift had a right to speak as one of authority.

Tom and his friend watched the aircraft for some time, and then started off in a long flight, attaining a high speed, which, at first, made Mr. Damon gasp, until he became used to it. He was no novice at flying, and had even operated aeroplanes himself, though at no great height.

Suddenly the Hawk seemed to falter, almost as does a bird stricken by a hunter's gun. The craft seemed to hang in the air, losing motion as though about to plunge to earth unguided.

"What's the matter?" cried Mr. Damon.

"One of the control wires broken!" was Tom's laconic answer. "I'll have to volplane down. Sit tight, there's no danger!"

Mr. Damon knew that with so competent a pilot as Tom Swift in the forward seat this was true, but, nevertheless, he was a bit nervous until he felt the smooth, gliding motion, with now and then an upward tilt, which showed that Tom was coming down from the upper regions in a series of long glides. The engine had stopped, and the cessation of the thundering noise made it possible for Tom and his passenger to talk without the use of the speaking tube.

"All right?" asked Mr. Damon.

"All right," Tom answered, and a little later the machine was rolling gently over the turf of a large field, a mile or so from the camp.

Before Tom and Mr. Damon could get out of their seats, a man, seemingly springing up from some hollow in the ground, walked toward them.

"Had an accident?" he asked, in what he evidently meant for a friendly voice.

"A little one, easily mended," Tom answered.

He was about to take off his goggles, but at sight of the man's face a change came over the countenance of Tom Swift, and he replaced the eye protectors. Then Tom turned to Mr. Damon, as if to ask a question, but the stranger came so close, evidently curious to see the aircraft at close quarters, that the young inventor could not speak without being overheard.

Tom got out his kit of tools to repair the broken control, and the man watched him curiously. As he tinkered away, something was stirring among the past memories of the inventor. A question he asked himself over and over again was:

"Where have I seen this man before? His face is familiar, but I can't place him. He is associated with something unpleasant. But where have I seen this man before?"